Answering whether white papers have any legal basis, I can only cover the UK with any certainty, but I would strongly suspect that my understanding is standard across the majority of countries,
Essentially white papers do not have any legal standing within the uk, and almost certainly the EU as that would not be in keeping with the medical device directive. From a design perspective I generally find them to contain heavily biased marketing drivel (at least commercial ones), which can at best be misleading. I understand they are more beneficial on the marketing side as they can give an understanding of the potential of a market, but you still have to question where the author gets the data and whether it is accurate.
Although white papers have no legal standing, government commissioned ones may in the longer term have an effect on a medical device business. Although the government (UK) cannot ignore the MDD, it can issue directions to the state run NHS and the various department of health quangos can write and commission their own white papers. I can't think of any examples of this though